Alphabetical list of windows
I tend to have a lot of windows open each with multiple tabs. When I look at the list of windows (under Windows in menu bar), I see the list of open windows in alphabetical order. When I switch to a new tab in an open window, the window list will be reordered, which drives me crazy. I want to display the open windows arranged in the order that I opened them rather than alphabetical. How do I turn off the alphabetizing?
To my knowledge, there is currently no way to change the ordering of the window entries in the Window menu. I just checked and Google Chrome behaves the same way, so Vivaldi likely inherits this behavior from Chromium. Safari and Opera behave the same way too, by the way (Firefox does not, though).
If you think that having an option for switching between the two behaviors is important, you can post this as a feature suggestion in this thread.
Here's another idea: There is a universal shortcut on macOS for quickly cycling through the windows of a given application (actually there are two: one for cycling 'forward' and one for cycling 'backward'). They differ based on your keyboard layout but you can find the 'forward' one for your system at "System Preferences->Keyboard->Shortcuts->Keyboard->Move focus to next window". For the 'backward' one, you just press Shift additionally.
With those shortcus, you can switch much faster between windows than you can by clicking on the Window menu and selecting one of the entries. I absolutely love those shortcuts and use them in every application that has more than one window.